Photoactivated ultralong room‐temperature phosphorescence from epoxy polymer films doped with carbazole derivatives for erasable light printing

The development of polymer‐based luminescent materials with efficient and switchable ultralong organic phosphorescence (UOP) under ambient conditions is of great importance but remains challenging. In this work, three new organic luminogens have been developed by attaching the ethyl benzoate to the nitrogen atoms of carbazole, 7H‐benzo[c]carbazole, and 7H‐dibenzo[c,g]carbazole via the Buchwald‐Hartwig coupling reaction, respectively. Subsequently, they are embedded into epoxy polymers through doping into the mixtures of bisphenol A diglycidyl ether and 1,3‐propylenediamine, followed by a thermal curing reaction. It is found that the resulting polymer films EB‐BCz@EP and EB‐2BCz@EP show unique photoactivated UOP properties. After UV light irradiation, their phosphorescence quantum yields are up to 7.6%, and the lifetimes reach 1.84 and 1.18 s, respectively. These observations suggest that it is possible to elevate the UOP lifetime without reducing the phosphorescence quantum yield by tuning the molecular structure of the guest luminogen. Upon thermal annealing, the photoactivated polymer films can recover to the pristine state, demonstrating switchable UOP characteristics of the polymer films in the air. Inspired by these exciting results, the EB‐2BCz@EP has been successfully explored as a transparent polymer film for erasable light printing.